ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 621 



development of a nervous organ must result in a rearrangement of all 

 the organs of the body, and may affect indifferent tissues. When this 

 happens new structures arise, which will owe the direction they take to 

 the organ that has caused them, which probably will itself become 

 larger and more complete. The formation of a central nervous organ 

 will cause a change not only in the already developed peripheral 

 nervous system, but in a number of indifferent ectodermal cells, which 

 will take on a nervous character and become united into new organs. 

 This process may be called that of substitution, and is not to be con- 

 founded with change of function, or with the process of the 

 physiological division of labour. 



Applying these considerations to the Annelids, and starting from 

 the Coelenterata, we find in the Annelid larva a nerve-ring and a 

 sensory epithelium. The organs of the latter gradually took on the 

 functions of the old nerve-ring, and became converted into more inde- 

 pendent organs. As the function of the primitive central organ 

 disappeared it became suppressed, and is only seen now in the organi- 

 zation of the larva. The notochord and vertebral column of the 

 vertebrata probably afford another example of this process of 

 substitution. 



Coral-reef Annelid.* — The Eev. T. Powell gives an account of the 

 structure and habits of Palolo viridis, in which he states his reasons for 

 considering as inaccurate the notion that the animals break up into 

 small pieces in order to effect the liberation of the egcs and of the 

 sperm. Their sight is evidently perfect. The time of their appear- 

 ance is the day of the last quarter of the moon in each October, unless 

 that fall at the beginning of the month, in which case another lunar 

 month will intervene. This indicates that the moon exercises some 

 mysterious influence on their reproduction. 



Muscular Tissue of the Leech.t — T. W. Shore finds that — 1. The 

 muscle of the leech consists of elongated tubes with two coats — a 

 sarcolemma and contractile layer — the inner surface of which is irre- 

 gular, and gives rise to apparently granular contents. 2. In the 

 living condition it is unstriped. 3. There are no nuclei. 4. Trans- 

 verse striation may be produced post-mortem, the result of three 

 changes : — a. Eegular arrangement of the papillae on the inner surface 

 of the contractile layer. (3. Folding of the surface of the sarcolemma. 

 8. Splitting into segments of the contractile substances which subse- 

 quently contract. 5. The contractile substance coagulates, forming 

 myosin, which subsequently contracts. 6. The rapidity of contraction 

 gives rise to varying appearances of fissures, striations, &c. 



Observations on the Dicyemidae. J — E. van Beneden gives us 

 the result of some further studies on these important fomis. He 

 commences by describing two new generic types, the first of which, 

 Conocyema polymorplia, lives with Dicyema typus in the renal cavity of 

 Sepia officinalis. It is not, however, nearly so common as its com- 



* Journ. Linn. Soc. (Zool.) xvi. (18S2) pp. 393-6. 

 t -Nature,' xxvi. (1882) pp. 493-4. 

 X Arch, de Biol., iii. (1882) pp. 195-228 (2 pla.). 

 Ser. 2.— Vol. II. 2 U 



